Calcium sparks in the intact gerbil spiral modiolar artery

Abstract

BackgroundCalcium sparks are ryanodine receptor mediated transient calcium signals that have been shown to hyperpolarize the membrane potential by activating large conductance calcium activated potassium (BK) channels in vascular smooth muscle cells. Along with voltage-dependent calcium channels, they form a signaling unit that has a vasodilatory influence on vascular diameter and regulation of myogenic tone. The existence and role of calcium sparks has hitherto been unexplored in the spiral modiolar artery, the end artery that controls blood flow to the cochlea. The goal of the present study was to determine the presence and properties of calcium sparks in the intact gerbil spiral modiolar artery.ResultsCalcium sparks were recorded from smooth muscle cells of intact arteries loaded with fluo-4 AM. Calcium sparks occurred with a frequency of 2.6 Hz, a rise time of 17 ms and a time to half-decay of 20 ms. Ryanodine reduced spark frequency within 3 min from 2.6 to 0.6 Hz. Caffeine (1 mM) increased spark frequency from 2.3 to 3.3 Hz and prolonged rise and half-decay times from 17 to 19 ms and from 20 to 23 ms, respectively. Elevation of potassium (3.6 to 37.5 mM), presumably via depolarization, increased spark frequency from 2.4 to 3.2 Hz. Neither ryanodine nor depolarization changed rise or decay times.ConclusionsThis is the first characterization of calcium sparks in smooth muscle cells of the spiral modiolar artery. The results suggest that calcium sparks may regulate the diameter of the spiral modiolar artery and cochlear blood flow.

Ryanodine-induced vasoconstriction of the gerbil spiral modiolar artery depends on the Ca2+ sensitivity but not on Ca2+ sparks or BK channels

“…Ca 2+ sparks and waves were recently reported in the intact unpressurized gerbil SMA [22]. We now report Ca 2+ sparks and Ca 2+ waves in SMCs of the pressurized gerbil SMA (Fig.…”

“…Ca 2+ sparks in the pressurized SMA occurred with a lower frequency than in unpressurized SMA [22], but with a similar frequency, spatial width and spark site density as observed in smooth muscle cells of cerebral pial arteries [15, 19, 28] and pressurized mesenteric arteries [21, 29]. The increase in Ca 2+ spark frequency in response to a 20 cmH 2 O (~ 14 mmHg) increase in pressure, is also consistent with observations made in cerebral arteries [28].…”

“…Typically, Ca 2+ spark sites are composed of 4 – 6 RyRs, giving a punctate staining pattern in immunolocalization studies. In the SMA, the distribution pattern of RyRs in SMCs shows a uniform expression throughout the SR rather than a punctate expression expected of ryanodine receptors clustered in spark sites [22] and may underlie the observed differences in the temporal properties and functional role of Ca 2+ sparks in the SMA.…”

“…We have recently demonstrated Ca 2+ sparks in smooth muscle cells of the intact SMA [22]. In this study, we investigate whether Ca 2+ sparks regulate the global Ca 2+ and vascular diameter in the SMA.…”

Primary Cultivation and Identification of Vascular Smooth Muscle Cells from the Spiral Modiolar Artery of Guinea Pigs

“…The blood flow is controlled effectively by the diameter of the blood vessel being regulated by the contractile activity of the SMCs [9]. However, the SMA cannot meet the requirements of related experiments, because it only has a single branch on each side, and the sample size is small [7]. Therefore, establishing a model of SMCs in vitro is highly significant to study the pathophysiological changes caused by disorders in the inner ear circulatory system and the etiological mechanism of relevant diseases.…”