Rhythmic variations in BKCa channel activity, [Ca2+]i level and PKC‐delta expression in rat cerebral arterial muscle cells (1070.6)

Abstract

Objectives: The objective of the present study is to investigate preence of rhythmic variation in KCa single‐channel activity, intracellular Ca2+ ([Ca2+]i ) level and PKC‐δ protein expression in rat cerebral arterial muscle cells.Methods. Although the underlying signaling mechanisms have not been elucidated yet, a circadian variation in the occurrence of cerebrovascular events and higher stroke incidence during morning hours has been reported. In the present study we investigated and compared changes in activities of a 238 pS Ca2+‐activated K+ channel (KCa) current, levels of intracellular Ca2+ ([Ca2+]i ) and PKC‐δ expression in freshly isolated rat cerebral arterial muscle cells during the early afternoon (2:00 PM) and in the early morning (2:00 AM) using the cell‐attached mode of the Patch Clamp technique, the ratiometric fluorescent dye Fura‐2AM to measure [Ca2+]i. and western blotting, respectively.Results. We found that the isolated cerebral arterial muscle cells exhibited altered NPo of a 238 pS KCa channel current (0.0038 ± 0.0004 at 2:00 PM and 0.0086 ± 0.0003 at 2:00 AM (n=5. P < 0.05) when recorded at a patch potential of +40 mV using symmetrical KCl solution, changed [Ca2+]i levels (172 ± 21 nM at 2:00 AM and 343 ± 76 nM at 2:00 PM, n= 3 trials, p < 0.05) and reduced expression of PKC‐δ protein at 2:00 AM compared to that determined at 2:00 PM of the day.Conclusions. Given that activities of KCa channel currents, [Ca2+]i level and PKC‐δ activity are requisite for the initiation and development of cerebral arterial myogenic tone, the observed rhythmic changes in these endogenous signaling events may be regarded as possible contributing factors for altered vascular reactivity and increased incidence of cerebral stroke at different times of the day.