Voltage-activated Ca2+ channels in rat renal afferent and efferent myocytes: No evidence for the T-type Ca2+ current

摘要

AimsBased on indirect methods, it has been suggested that both L-and T-type Ca2+ channels mediate signalling in the renal afferent arteriole and that T-type Ca2+ channels are involved in signalling in the efferent arteriole. However, Ca2+ currents have never been studied in these two vessels. Our study was initiated to directly determine the type of Ca 2+ channels in these vessels for the first time, using patch clamp.Methods and resultsNative myocytes were obtained from individually isolated rat renal afferent and efferent arterioles and from rat tail arteries (TA). TA myocytes, which possess both L-and T-type Ca2+ currents, served as a positive control. Inward Ca2+ and Ba2+ currents (ICa and IBa) were measured in 1.5 mmol/L Ca 2+ and 10 mmol/L Ba2+, respectively, using the whole-cell configuration. By exploiting known differences in activation and inactivation characteristics and differing sensitivities to nifedipine and kurtoxin, the presence of both L-and T-type Ca2+ channels in TA myocytes was readily demonstrated. Afferent arteriolar myocytes exhibited relatively large ICa densities (-2.0 ± 0.2 pA/pF) in physiological Ca 2+ and the IBa was 3.6-fold greater. These currents were blocked by nifedipine, but not by kurtoxin, and did not exhibit the activation and inactivation characteristics of T-type Ca2+ channels. Efferent arteriolar myocytes did not exhibit a discernible voltage-activated I Ca in physiological Ca2+.ConclusionOur findings support the physiological role of L-type Ca2+ channels in the afferent, but not efferent, arteriole, but do not support the premise that functional T-type Ca2+ channels are present in either vessel.