Cobalt ions enhance light responsiveness of carp cone horizontal cells in low calcium.
Effects of cobalt ions (Co2+) on horizontal cells in low extracellular calcium were examined in isolated, superfused carp retinas. While 0.1 mmol/L Co2+ completely suppressed both rod- and cone-driven horizontal cells in normal Ringer's solution, it enhanced light responses of cone horizontal cells in low (0.1 mmol/L) calcium. The enhancement of the cone horizontal cell response by Co2+ was not caused by changes in light responsiveness of cone photoreceptors. Moreover, application of 50 mumol/L IBMX, an inhibitor of phosphodiester enzyme, reduced the suppressive effect of 0.1 mmol/L Co2+ in normal Ringer's solution. In consequence, the above-described enhancement of the cone horizontal cell light responsiveness may be due to a depolarization of cones caused by low calcium, which increases the activity of voltage-dependent calcium channels at cone terminals.
Wang
H
H
Shanghai Institute of Physiology, Joint Laboratory of Life Sciences, Chinese Academy of Sciences, China.
Yang
X
X
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002347:Carps / Q000502:physiology*; D003035:Cobalt / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010775:Photic Stimulation; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology / Q000502:physiology*
D010726:Phosphodiesterase Inhibitors; D003035:Cobalt; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine