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, [Ca 2+ ] i . The mean control [Ca 2+ ] i was 55 nM in isolated cells and 67 nM in clusters. The following procedures changed [Ca 2+ ] i : (1) 0[Ca 2+ ] o +EGTA reduced [Ca 2+ ] i by about 50%, suggesting that the remaining calcium originated from intracellular organelles. [Ca 2+ ] i increased when [Ca 2+ ] o was doubled. (2) Hypoxia by sodium dithionite (Na 2 S 2 O 4 ) induced large [Ca 2+ ] i increases in clustered and isolated cells. Smaller rises occurred with 100% N 2 hypoxia. The augmented [Ca 2+ ] i , induced by Na 2 S 2 O 4 , was reduced (not eliminated) in 0[Ca 2+ ] o +EGTA, suggesting that some calcium was intracellularly released. Nifedipine depressed (did not block) the Na 2 S 2 O 4 -induced calcium increase, implying some inflow via other (N, T or P/Q) voltage-dependent or voltage-independent calcium channels. (3) Cholinergic agents (ACh, nicotine, muscarine, bethanechol and pilocarpine) increased [Ca 2+ ] i . The ACh effect was produced exclusively by calcium inflow since it was eliminated in 0[Ca 2+ ] o +EGTA. Cholinergic effects were depressed (not obliterated) by d -tubocurarine ( d -TC), hexamethonium (C6) and atropine. (4) ACh, nicotine and pilocarpine potentiated the excitatory effect of Na 2 S 2 O 4 on [Ca 2+ ] i . Bethanechol depressed this excitation whereas muscarine had inconsistent effects. (5) Atropine and C6 depressed [Ca 2+ ] i increases elicited by Na 2 S 2 O 4 but the effects of d -TC were variable. (6) Dopamine (DA) had variable effects. It increased [Ca 2+ ] i in 75% of cases, and reduced the Na 2 S 2 O 4 -induced calcium increase. Thus, calcium increases during Na 2 S 2 O 4 occur by direct effects on the glomus cells and feedback action through released ACh and DA.