Effects of the protein tyrosine phosphatase inhibitor phenylarsine oxide on excision-activated calcium channels in Lymnaea neurons

Abstract

Most calcium channels are tightly regulated, closed in the resting cell, and open only in response to specific physiological signals such as depolarization or binding of a particular ligand. In addition, calcium permeable channels which can be activated experimentally by excising a small patch of plasma membrane from the cell have been described in several preparations, including neurons and cardiac muscle. Little is known about possible physiological regulators of these channels. We examined an excision-activated calcium channel from neurons of the pond snail Lymnaea stagnalis. This channel, the ‘HP channel’, is divalent selective and voltage-independent. In this report, we show that excision activation can occur very rapidly (within 200–400 ms after patch excision), and that this activity can be at least partially inhibited by `cramming' the isolated membrane patch back into the cell's cytoplasm. We also show that excision activation is inhibited in cells which have been pretreated with inhibitors of protein tyrosine phosphatases, either pervanadate (0.5 mM) or phenylarsine oxide (1–7 μM). The effect of phenylarsine oxide is not seen in cells which have been pretreated with tyrosine kinase inhibitors (genistein or herbimycin A). The results suggest that tyrosine phosphorylation signalling pathways may play a role in the physiological regulation of these channels.