Pimaric Acid (PiMA). A Novel Opener of KCa1.1 Channels. PiMA was found to be a potent opener of Kca1.1 (large conductance Ca2+ activated K+ (BK)) channels. 1μM PiMA doubled the current carried via BK channels and this effect increased dose dependently. PiMA increases the open probability of single BK channels by shifting both its voltage and Ca2+ dependence to more hyperpolarized voltages. BK channels that were activated by PiMA retain their charybdotoxin sensitivity.