We have investigated in Xenopus oocytes the effects of phorbol ester-induced protein kinase C (PKC) stimulation on dihydropyridine (DHP)-insensitive and -sensitive Ca 2 + channels. DHP-insensitive Ba 2 + currents (I B a ) were recorded from endogenous channels in non-injected oocytes and in oocytes injected with cRNAs encoding the auxiliary rabbit α 2 /δ and β 1 Ca 2 + channel subunits. A human α 1 C cRNA, injected alone or in combination with cRNAs of the auxiliary subunits, was used for studying DHP-sensitive I B a . We found that DHP-insensitive I B a was increased by 4β-phorbol 12-myristate 13-acetate (PMA), while DHP-sensitive I B a was decreased. In both cases, the effects depended only on the co-expression of the β 1 subunit.