Effects of hypoxia and putative transmitters on [Ca2+]i of rat glomus cells.

Dissociated rat glomus cells were loaded with Fura-2 AM to study the effects of hypoxia, and carotid body transmitters on intracellular calcium, [Ca2+]i. The mean control [Ca2+]i was 55 nM in isolated cells and 67 nM in clusters. The following procedures changed [Ca2+]i:0[Ca2+]o+EGTA reduced [Ca2+]i by about 50%, suggesting that the remaining calcium originated from intracellular organelles. [Ca2+]i increased when [Ca2+]o was doubled. Hypoxia by sodium dithionite (Na2S2O4) induced large [Ca2+]i increases in clustered and isolated cells. Smaller rises occurred with 100% N2 hypoxia. The augmented [Ca2+]i, induced by Na2S2O4, was reduced (not eliminated) in 0[Ca2+]o+EGTA, suggesting that some calcium was intracellularly released. Nifedipine depressed (did not block) the Na2S2O4-induced calcium increase, implying some inflow via other (N, T or P/Q) voltage-dependent or voltage-independent calcium channels.Cholinergic agents (ACh, nicotine, muscarine, bethanechol and pilocarpine) increased [Ca2+]i. The ACh effect was produced exclusively by calcium inflow since it was eliminated in 0[Ca2+]o+EGTA. Cholinergic effects were depressed (not obliterated) by D-tubocurarine (D-TC), hexamethonium (C6) and atropine.ACh, nicotine and pilocarpine potentiated the excitatory effect of Na2S2O4 on [Ca2+]i. Bethanechol depressed this excitation whereas muscarine had inconsistent effects. Atropine and C6 depressed [Ca2+]i increases elicited by Na2S2O4 but the effects of D-TC were variable. Dopamine (DA) had variable effects. It increased [Ca2+]i in 75% of cases, and reduced the Na2S2O4 -induced calcium increase.Thus, calcium increases during Na2S2O4 occur by direct effects on the glomus cells and feedback action through released ACh and DA.