In the presence of 10(-9) M calcium, rod outer segments freshly detached from dark-adapted frog retinas contain between 0.01 and 0.02 moles of guanosine 3',5'-cyclic monophosphate (cyclic GMP) per mole of rhodopsin. The dark level of cyclic GMP is reduced approximately 50% by illumination that bleaches 5 x 10(5) rhodopsin molecules/outer segments. The dark levels of cyclic GMP also can be suppressed to approximately 0.007 mol/mol of rhodopsin by increasing the concentration of calcium from 10(-9) M to 2 x 10(-9) M, and they remain at this level as calcium concentration is raised to 10(-3) M. The final level to which illumination reduces cyclic GMP in unaffected by the calcium concentration between 10(-9) and 10(-3) M. The maximal light-induced decrease in cyclic GMP occurs within 1 s from the onset of illumination at all calcium concentrations. The magnitude and time-course of the light-induced decrease in cyclic GMP measured in these experiments are comparable to values obtained previously (Woodruff et al. 1977. J. Gen. Physiol. 69:677-679; Woodruff and Bownds. 1979. J. Gen. Physiol. 73:629-653). The data are consistent with a role for cyclic GMP in visual transduction irrespective of the calcium concentration.
Article| January 01 1981
Influence of calcium on guanosine 3',5'-cyclic monophosphate levels in frog rod outer segments.
A S Polans
M D Bownds
Online ISSN: 1540-7748
Print ISSN: 0022-1295
J Gen Physiol (1981) 77 (1): 41–48.
A S Polans, S Kawamura, M D Bownds; Influence of calcium on guanosine 3',5'-cyclic monophosphate levels in frog rod outer segments.. J Gen Physiol 1 January 1981; 77 (1): 41–48. doi: https://doi.org/10.1085/jgp.77.1.41
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