CA2-BODY GLOMUS CELLS IS CONDUCTED BY MULTIPLE TYPES OF HIGH-VOLTAGE-ACTIVATED CA2+ CHANNELS( CURRENT IN RABBIT CAROTID)

Carotid bodies are sensory organs that detect changes in arterial oxyg en. Glomus cells are presumed to be the initial sites for sensory tran sduction, and Ca2+-dependent neurotransmitter release from glomus cell s is believed to be an obligatory step in this response. Some informat ion exists on the Ca2+ channels in rat glomus cells. However, relative ly Little is known about the types of Ca2+ channels present in rabbit glomus cells, the species in which most of the neurotransmitter releas e studies have been performed. Therefore we tested the effect of speci fic Ca2+ channel blockers on current recorded from freshly dissociated , adult rabbit carotid body glomus cells using the whole cell configur ation of the patch-clamp technique. Macroscopic Ba2+ current elicited from a holding potential of -80 mV activated at a V-m of approximaely -30 mV, peaked between 0 and +10 mV and did not inactivate during 25-m s steps to positive test potentials. Prolonged (approximate to 2 min) depolarized holding potentials inactivated the current with a V-1/2 of -47 mV. There was no evidence for T-type channels. On steps to 0 mV, 6 mM Co2+ decreased peak inward current by 97 +/- 1% (mean +/- SE). Ni soldipine (2 mu M), 1 mu M omega-conotoxin GVIA, and 100 nM omega-agat oxin IVa each blocked a portion of the macroscopic Ca2+ current (30 +/ - 5, 33 +/- 5, and 19 +/- 3% after rundown correction, respectively). Simultaneous application of these blockers revealed a resistant curren t that was not affected by 1 mu M omega-conotoxin MVIIC. This resistan t current constituted 27 +/- 5% of the total macroscopic Ca2+ current. Each blocker had an effect in every cell so tested. However, the rela tive proportion of current blocked varied from cell to cell. These res ults suggest that L, N, P, and resistant channel types each conduct a significant proportion of the macroscopic Ca2+ current in rabbit glomu s cells. Hypoxia-induced neurotransmitter release from glomus cells ma y involve one or more of these channels.