Ca²⁺sparks and BK currents in gallbladder myocytes: role in CCK-induced response

Abstract

Pozo, María J., Guillermo J. Pé rez, Mark T. Nelson, and Gary M. Mawe. Ca 2ϩ sparks and BK currents in gallbladder myocytes: role in CCK-induced response. Am J Physiol Gastrointest Liver Physiol 282: G165-G174, 2002. First published October 24, 2001 10.1152/ajpgi.00326. 2002We sought to elucidate the regulation of gallbladder smooth muscle (GBSM) excitability by localized Ca 2ϩ release events (sparks) and large-conductance Ca 2ϩ -dependent (BK) channels by determining whether sparks exist in GBSM and, if so, whether they activate BK channels. Sparks were identified in isolated GBSM loaded with fluo 4. Each spark was associated with a transient outward current, suggesting communication of ryanodine receptor (RyR) channels with BK channels. This was confirmed by the inhibition of outward currents with iberiotoxin (100 nM), thapsigargin (200 nM), and ryanodine (10 M). In current clamp mode, the transient BK currents were associated with brief membrane hyperpolarizations (10.9 Ϯ 1.3 mV). Because transient BK currents could dampen GBSM excitability, we tested whether CCK attenuates these events. CCK (10 nM) reduced the amplitude and frequency of transient BK currents, and subsequent caffeine application restored transient BK current activity. These results support the concept that RyRs and BK channels contribute to the regulation of GBSM excitability and that CCK can act in part by inhibiting this pathway.

Role of mitochondria in spontaneous rhythmic activity and intracellular calcium waves in the guinea pig gallbladder smooth muscle

“…Ca 2ϩ -activated K ϩ channels are present in GBSM and are involved with reducing excitability through a hyperpolarization (28,34,54), which may explain the tendency for plasma membrane hyperpolarization observed in some GBSM immediately after the application of CCCP. It is also possible that CCCP and FCCP reduced APs and Ca 2ϩ flashes through transient activation of other types of potassium channels known to exist in GBSM (17,31,34,54).…”

“…Furthermore, we have previously demonstrated that VDCC and nonselective cation channels in the plasma membrane (27,30,33,54) and the SR (2,3,27,34) are also essential for rhythmic activity in the GBSM. Collectively, these findings indicate that the mitochondrion, SR, and plasma membrane channels constitute key components of the GBSM pacemaker.…”

“…Cells with the morphological features of ICC have also been reported recently in the murine (43) and human (13) sparks, play a fundamental role in GBSM rhythmic activity (2,27,34). These findings correspond with observations in GI tract (49,50) and suggest that intracellular Ca 2ϩ mobilization, involving both SR and mitochondria, may be essential for the generation and propagation of rhythmic electrical activity in the gallbladder as has been observed in the GI tract (15, 38, 48 -52) and the urinary bladder (19).…”

Melatonin Treatment Reverts Age-Related Changes in Guinea Pig Gallbladder Neuromuscular Transmission and Contractility

“…Gallbladder smooth muscle cells were dissociated enzymatically using a previously described method (Pozo et al, 2002). In brief, the gallbladder was cut into small pieces and incubated for 34 min at 37°C in enzyme solution (for composition see Solutions and Drugs) supplemented with 1 mg/ml bovine serum albumin (BSA), 1 mg/ml papain, and 1 mg/ml 1,4-dithio-DL-threitol.…”

A BK (Slo1) channel journey from molecule to physiology

“…191 Furthermore, a similar coupling mechanism between Ca 2+ sparks and BK channel activity was demonstrated in gallbladder myocytes. 192 Thus, inhibition and/or downregulation of BK channels could be the cause of smooth muscle cell contractility alteration, as found in urinary bladder overactivity. 193 In brief, despite tissue and interspecies diversity, a general behavior can be observed as a common factor for BK contribution to cell physiology.…”