Alteration of the ligand sensitivity in human cone CNG channel by rod monochromacy-associated mutations in hCNGA3

Abstract

The human cone cyclic nucleotide-gated (CNG) channel comprises hCNGA3 α-subunit and hCNGB3 β-subunit. Mutations in both hCNGA3 and hCNGB3 have been linked to rod monochromacy. In the present study we examined the functional consequences of the rod monochromacy-associated T565M and E593K mutations in hCNGA3, which reside in the cyclic nucleotide-binding domains (CNBD) of the α-subunit. Macroscopic patch current was recorded from HEK293T cells expressing the recombinant CNG channels using the inside-out patch-clamp methods. The apparent affinity for cGMP (160 μM) in hCNGA3 homomeric channels containing the T565M mutation was markedly lower than that (9.0 μM) in wild-type hCNGA3 channels. On the other hand, hCNGA3 channels containing the E593K mutation exhibited a significantly higher apparent affinity for cGMP (3.0 μM) compared with wild-type hCNGA3 channels. When the hCNGA3 was associated with the hCNGB3, the apparent affinity for cGMP was significantly reduced (15.0 μM). However, association of the hCNGA3 containing the T565M or E593K mutation with the hCNGB3 did not appreciably affect the apparent affinity for cGMP. The present results thus suggest that the rod monochromacy-associated mutations (T565M and E593K) in the hCNGA3 lead to a marked alteration in the sensitivity for cGMP in human cone CNG channels and thereby contribute at least partly to the pathogenesis of rod monochromacy. [Jpn J Physiol 54 Suppl:S136 (2004)]