diff --git a/google/cloud/pubsub_v1/publisher/client.py b/google/cloud/pubsub_v1/publisher/client.py
index f1e198b1a..f1de9f1f4 100644
--- a/google/cloud/pubsub_v1/publisher/client.py
+++ b/google/cloud/pubsub_v1/publisher/client.py
@@ -130,15 +130,19 @@ def __init__(self, batch_settings=(), publisher_options=(), **kwargs):
                 target=os.environ.get("PUBSUB_EMULATOR_HOST")
             )
 
+        # The GAPIC client has mTLS logic to determine the api endpoint and the
+        # ssl credentials to use. Here we create a GAPIC client to help compute the
+        # api endpoint and ssl credentials. The api endpoint will be used to set
+        # `self._target`, and ssl credentials will be passed to
+        # `grpc_helpers.create_channel` to establish a mTLS channel (if ssl
+        # credentials is not None).
         client_options = kwargs.get("client_options", None)
-        if (
-            client_options
-            and "api_endpoint" in client_options
-            and isinstance(client_options["api_endpoint"], six.string_types)
-        ):
-            self._target = client_options["api_endpoint"]
-        else:
-            self._target = publisher_client.PublisherClient.SERVICE_ADDRESS
+        credentials = kwargs.get("credentials", None)
+        client_for_mtls_info = publisher_client.PublisherClient(
+            credentials=credentials, client_options=client_options
+        )
+
+        self._target = client_for_mtls_info._transport._host
 
         # Use a custom channel.
         # We need this in order to set appropriate default message size and
@@ -149,6 +153,7 @@ def __init__(self, batch_settings=(), publisher_options=(), **kwargs):
                 channel = grpc_helpers.create_channel(
                     credentials=kwargs.pop("credentials", None),
                     target=self.target,
+                    ssl_credentials=client_for_mtls_info._transport._ssl_channel_credentials,
                     scopes=publisher_client.PublisherClient._DEFAULT_SCOPES,
                     options={
                         "grpc.max_send_message_length": -1,
diff --git a/google/cloud/pubsub_v1/subscriber/client.py b/google/cloud/pubsub_v1/subscriber/client.py
index e0b10c888..e33a0e2e6 100644
--- a/google/cloud/pubsub_v1/subscriber/client.py
+++ b/google/cloud/pubsub_v1/subscriber/client.py
@@ -16,7 +16,6 @@
 
 import os
 import pkg_resources
-import six
 
 import grpc
 
@@ -82,16 +81,19 @@ def __init__(self, **kwargs):
                 target=os.environ.get("PUBSUB_EMULATOR_HOST")
             )
 
-        # api_endpoint wont be applied if 'transport' is passed in.
+        # The GAPIC client has mTLS logic to determine the api endpoint and the
+        # ssl credentials to use. Here we create a GAPIC client to help compute the
+        # api endpoint and ssl credentials. The api endpoint will be used to set
+        # `self._target`, and ssl credentials will be passed to
+        # `grpc_helpers.create_channel` to establish a mTLS channel (if ssl
+        # credentials is not None).
         client_options = kwargs.get("client_options", None)
-        if (
-            client_options
-            and "api_endpoint" in client_options
-            and isinstance(client_options["api_endpoint"], six.string_types)
-        ):
-            self._target = client_options["api_endpoint"]
-        else:
-            self._target = subscriber_client.SubscriberClient.SERVICE_ADDRESS
+        credentials = kwargs.get("credentials", None)
+        client_for_mtls_info = subscriber_client.SubscriberClient(
+            credentials=credentials, client_options=client_options
+        )
+
+        self._target = client_for_mtls_info._transport._host
 
         # Use a custom channel.
         # We need this in order to set appropriate default message size and
@@ -102,6 +104,7 @@ def __init__(self, **kwargs):
                 channel = grpc_helpers.create_channel(
                     credentials=kwargs.pop("credentials", None),
                     target=self.target,
+                    ssl_credentials=client_for_mtls_info._transport._ssl_channel_credentials,
                     scopes=subscriber_client.SubscriberClient._DEFAULT_SCOPES,
                     options={
                         "grpc.max_send_message_length": -1,
diff --git a/tests/unit/pubsub_v1/publisher/test_publisher_client.py b/tests/unit/pubsub_v1/publisher/test_publisher_client.py
index 3b6aa1477..0f661c2fa 100644
--- a/tests/unit/pubsub_v1/publisher/test_publisher_client.py
+++ b/tests/unit/pubsub_v1/publisher/test_publisher_client.py
@@ -18,6 +18,7 @@
 import inspect
 
 from google.auth import credentials
+import grpc
 
 import mock
 import pytest
@@ -81,7 +82,7 @@ def test_init_w_api_endpoint():
     assert isinstance(client.api, publisher_client.PublisherClient)
     assert (client.api._transport.grpc_channel._channel.target()).decode(
         "utf-8"
-    ) == "testendpoint.google.com"
+    ) == "testendpoint.google.com:443"
 
 
 def test_init_w_unicode_api_endpoint():
@@ -91,7 +92,7 @@ def test_init_w_unicode_api_endpoint():
     assert isinstance(client.api, publisher_client.PublisherClient)
     assert (client.api._transport.grpc_channel._channel.target()).decode(
         "utf-8"
-    ) == "testendpoint.google.com"
+    ) == "testendpoint.google.com:443"
 
 
 def test_init_w_empty_client_options():
@@ -104,8 +105,13 @@ def test_init_w_empty_client_options():
 
 
 def test_init_client_options_pass_through():
+    mock_ssl_creds = grpc.ssl_channel_credentials()
+
     def init(self, *args, **kwargs):
         self.kwargs = kwargs
+        self._transport = mock.Mock()
+        self._transport._host = "testendpoint.google.com"
+        self._transport._ssl_channel_credentials = mock_ssl_creds
 
     with mock.patch.object(publisher_client.PublisherClient, "__init__", init):
         client = publisher.Client(
@@ -119,6 +125,8 @@ def init(self, *args, **kwargs):
         assert client_options.get("quota_project_id") == "42"
         assert client_options.get("scopes") == []
         assert client_options.get("credentials_file") == "file.json"
+        assert client.target == "testendpoint.google.com"
+        assert client.api.transport._ssl_channel_credentials == mock_ssl_creds
 
 
 def test_init_emulator(monkeypatch):
diff --git a/tests/unit/pubsub_v1/subscriber/test_subscriber_client.py b/tests/unit/pubsub_v1/subscriber/test_subscriber_client.py
index 634351757..d56289276 100644
--- a/tests/unit/pubsub_v1/subscriber/test_subscriber_client.py
+++ b/tests/unit/pubsub_v1/subscriber/test_subscriber_client.py
@@ -13,6 +13,7 @@
 # limitations under the License.
 
 from google.auth import credentials
+import grpc
 import mock
 
 from google.cloud.pubsub_v1 import subscriber
@@ -42,7 +43,7 @@ def test_init_w_api_endpoint():
     assert isinstance(client.api, subscriber_client.SubscriberClient)
     assert (client.api._transport.grpc_channel._channel.target()).decode(
         "utf-8"
-    ) == "testendpoint.google.com"
+    ) == "testendpoint.google.com:443"
 
 
 def test_init_w_unicode_api_endpoint():
@@ -52,7 +53,7 @@ def test_init_w_unicode_api_endpoint():
     assert isinstance(client.api, subscriber_client.SubscriberClient)
     assert (client.api._transport.grpc_channel._channel.target()).decode(
         "utf-8"
-    ) == "testendpoint.google.com"
+    ) == "testendpoint.google.com:443"
 
 
 def test_init_w_empty_client_options():
@@ -65,8 +66,13 @@ def test_init_w_empty_client_options():
 
 
 def test_init_client_options_pass_through():
+    mock_ssl_creds = grpc.ssl_channel_credentials()
+
     def init(self, *args, **kwargs):
         self.kwargs = kwargs
+        self._transport = mock.Mock()
+        self._transport._host = "testendpoint.google.com"
+        self._transport._ssl_channel_credentials = mock_ssl_creds
 
     with mock.patch.object(subscriber_client.SubscriberClient, "__init__", init):
         client = subscriber.Client(
@@ -80,6 +86,8 @@ def init(self, *args, **kwargs):
         assert client_options.get("quota_project_id") == "42"
         assert client_options.get("scopes") == []
         assert client_options.get("credentials_file") == "file.json"
+        assert client.target == "testendpoint.google.com"
+        assert client.api.transport._ssl_channel_credentials == mock_ssl_creds
 
 
 def test_init_emulator(monkeypatch):