A CYSTEINE-RICH DOMAIN DEFINED BY A NOVEL EXON IN A SLO VARIANT IN RAT ADRENAL CHROMAFFIN CELLS AND PC12 CELLS

cDNA libraries from rat chromaffin cells and PC12 cells were screened for homologs to the mouse mSlo gene that encodes a large conductance, calcium (Ca2+)- and voltage-activated potassium channel (BK channel). One Slo variant contained sequence encoding a cysteine-rich, 59-amino acid insert for a previously described site of alternative splicing. T his insert is reminiscent of zinc-finger domains. The exon was found i n RNA from pancreas, anterior pituitary, cerebellum, and hippocampus. Expression in Xenopus oocytes of a Slo construct containing this exon conferred a -30 to -20 mV shift of the conductance-voltage curve. A pr eviously uncharacterized alternative splice junction near the C-termin al end of Slo was also identified. In contrast to BK channels in rat c hromaffin cells, none of the Sb variants exhibited inactivation when e xpressed in Xenopus oocytes, PCR screening of chromaffin cell RNA fail ed to reveal a homolog of an accessory beta subunit known to influence Slo channel function, Furthermore, a beta-subunit-dependent Slo chann el activator, dehydrosoyasaponin I, was without effect on chromaffin c ell BK current. The results argue that an accessory subunit may not be a required component of the native chromaffin cell BK channel.