L- and N-type Ca2+ channels in adult rat carotid body chemoreceptor type I cells.

1. Whole-cell voltage-dependent Ca2+ currents recorded from chemoreceptor type I cells of the adult rat carotid body had maximum amplitudes of -94 pA in 10 mM Ca2+ and were half-inactivated at a holding potential of -38 mV. Somatostatin and dopamine inhibited whole-cell Ca2+ current in type I cells. 2. The dihydropyridine agonist (+)202-791 increased the Ca2+ current amplitude by 106% at a step potential of -18 mV. The dihydropyridine antagonist nimodipine decreased the Ca2+ current amplitude by 40% from a holding potential of -80 mV, and by 74% from a holding potential of -60 mV. The nimodipine-sensitive current had a maximum amplitude at a membrane potential of -12 mV. omega-Conotoxin GVIA (omega-CgTX GVIA) blocked the whole-cell Ca2+ current by 40%. The omega-CgTX GVIA-sensitive current had a maximum amplitude at a membrane potential of +2 mV. 3. In summary, type I cells of the adult rat carotid body have dihydropyridine-sensitive L-type and omega-conotoxin GVIA-sensitive N-type voltage-dependent Ca2+ channels. These channels may play a role in the voltage-gated entry of Ca2+ necessary for stimulus-secretion coupling in response to changes in arterial PO2, PCO2 and pH. Inhibition of the Ca2+ currents by somatostatin and dopamine may alter the chemotransduction signal in type I cells.