The cytosolic II–III loop of Cav2.3 provides an essential determinant for the phorbol ester‐mediated stimulation of E–type Ca2+ channel activity

There is growing evidence that E-type voltage dependent Ca 2 + channels (Ca v 2.3) are involved in triggering and controlling pivotal cellular processes like neurosecretion and long-term potentiation. The mechanism underlying a novel Ca 2 + dependent stimulation of E-type Ca 2 + channels was investigated in the context of the recent finding that influx of Ca 2 + through other voltage dependent Ca 2 + channels is necessary and sufficient to directly activate protein kinase C (PKC). With Ba 2 + as charge carrier through Ca v 2.3 channel α 1 subunits expressed in HEK-293 cells, activation of PKC by low concentrations of phorbol ester augmented peak I B a by approximately 60%. In addition, the non-inactivating fraction of I B a was increased by more than three-fold and recovery from short-term inactivation was accelerated. The effect of phorbol ester on I B a was inhibited by application of the specific PKC inhibitor bisindolylmaleimide I. With Ca 2 + as charge carrier, application of phorbol ester did not change the activity of Ca v 2.3 currents but they were modified by the PKC inhibitor bisindolylmaleimide I. These results suggest that with Ca 2 + as charge carrier the incoming Ca 2 + can activate PKC, thereby augmenting Ca 2 + influx into the cytosol. No modulation of Ca v 2.3 channels by PKC was observed when an arginine rich region in the II-III loop of Ca v 2.3 was eliminated. Receptor independent stimulation of PKC and its interaction with Ca v 2.3 channels therefore represents an important positive feedback mechanism to decode electrical signals into a variety of cellular functions.