Anion modulation of calcium current voltage dependence and amplitude in salamander rods

Hofmeister anions were used to investigate the ability of Cl- replacement t o produce inhibition and a hyperpolarizing activation shift in L-type Ca2currents (I-Ca) of rod photoreceptors. Inhibition of I-Ca largely followed the Hofmeister sequence: Cl- = Br- < NO3- < I- < ClO4- (ClO4- caused the gr eatest suppression). Anion-induced hyperpolarizing activation shifts also f ollowed the Hofmeister sequence: Cl- < Br- < NO3- < I- < ClO4- (ClO4- cause d the largest shift). Agreement with the Hofmeister sequence suggests that these effects are due to anion interactions at the membrane surface. Hofmei ster anions also caused similar hyperpolarizing shifts in the voltage depen dence of inwardly rectifying cation currents (I-h) and outward K+ currents (I-K) consistent with the hypothesis that hyperpolarizing shifts arise from anion effects on membrane surface potential. Sulfate and phosphate inhibit ed rod I-Ca and phosphate caused a significant leftward activation shift su ggesting these anions are strongly adsorbed to the membrane. Because of the overlap between the physiological voltage range and the lower part of the I-Ca activation curve, anion effects on amplitude and activation may influe nce synaptic transmission at the first retinal synapse. (C) 2000 Elsevier S cience B.V. All rights reserved.