Functional analysis of congenital stationary night blindness type-2 CACNA1F mutations F742C, G1007R, and R1049W

Congenital stationary night blindess-2 (incomplete congenital stationary night blindness (iCSNB) or CSNB-2) is a nonprogressive, X-linked retinal disease which can lead to clinical symptoms such as myopia, hyperopia, nystagmus, strabismus, decreased visual acuity, and impaired scotopic vision. These clinical manifestations are linked to mutations found in the CACNA1F gene which encodes for the Cav1.4 voltage-gated calcium channel. To better understand the physiological effects of these mutations, three missense mutants, F742C, G1007R and R1049W, previously shown to be mutated in patients with CSNB-2, were transiently expressed in human embryonic kidney (HEK) tsA-201 cells and characterized using whole-cell patch clamp. The G1007R mutation is located in transmembrane segment 5 (S5) of domain III and R1049W is located in the extracellular linker between S5 and the P-loop of domain III. Both mutants produced full length proteins that targeted to the membrane but did not support ionic currents. In 20 mM Ba2+, F742C (S6 domain II) produced a ∼21 mV hyperpolarizing shift in half activation potential (Va[1/2]) and a ∼23 mV hyperpolarizing shift in half inactivation potential (Vh[1/2]). Additionally, F742C displayed slower inactivation kinetics and a smaller whole cell conductance (Gmax). In physiological 2 mM Ca2+, F742C produced a ∼19 mV hyperpolarizing shift in Va[1/2]. These findings suggest that the pathology of CSNB-2 in patients with these missense mutations in the Cav1.4 calcium channel is the result in either a gain of function (F742C) or a loss of function (G1007R, R1049W).