Ca2+ modulation of the cGMP-gated channel of bullfrog retinal rod photoreceptors.
1. The outer segment of an isolated rod photoreceptor from the bullfrog retina was drawn into a pipette containing choline solution for recording membrane current. The rest of the cell was sheared off with a glass probe to allow internal dialysis of the outer segment with a bath potassium solution ('truncated rod outer segment' preparation). The potential between the inside and the outside of the pipette was held at 0 mV. 2. Application of bath cGMP, in the presence of 3-isobutyl-1-methylxanthine (IBMX), gave rise to an outward membrane current. At saturating cGMP concentrations, this current was insensitive to intracellular Ca2+ at concentrations between 0 and 10 microM. At subsaturating cGMP concentrations, however, this current was inhibited by intracellular Ca2+. This sensitivity to Ca2+ declined after dialysis with a low-Ca2+ solution, suggesting the involvement of a soluble factor. 3. At low (nominally 0) Ca2+, the half-maximal activation constant and Hill coefficient for the activation of the cGMP-gated current by cGMP were 27 microM and 2.0, respectively. At high (ca 10 microM) Ca2+, the corresponding values were 40 microM cGMP and 2.4. 4. The inhibition of the current by Ca2+ was characterized at 20 microM cGMP. Ca2+ inhibited the current by up to 60%, with half-maximal inhibition at 48 nM Ca2+ and a Hill coefficient of 1.6.
Nakatani
K
K
Institute of Biological Sciences, University of Tsukuba, Ibaraki, Japan.
Koutalos
Y
Y
Yau
K W
KW
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D006152:Cyclic GMP / Q000494:pharmacology*; D054815:Cyclic Nucleotide-Gated Cation Channels; D004305:Dose-Response Relationship, Drug; D007473:Ion Channels / Q000187:drug effects* / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D011892:Rana catesbeiana; D017948:Retinal Rod Photoreceptor Cells / Q000187:drug effects*; D013997:Time Factors
D054815:Cyclic Nucleotide-Gated Cation Channels; D007473:Ion Channels; D006152:Cyclic GMP; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine