Regulation of basal intracellular calcium concentration by the sarcoplasmic reticulum in myocytes from the rat gastric antrum

• Published in: The Journal of physiology 2000-12, Vol.529 (2), p.395-404
• Main Authors: White, C., McGeown, J. G.
• Format: Article
• Language: English
• Subjects: Animals; Calcium - metabolism; Calcium-Transporting ATPases - antagonists & inhibitors; Carbachol - pharmacology; Cholinergic Agonists - pharmacology; Cytoplasm - metabolism; Indoles - pharmacology; Male; Manganese - metabolism; Muscle, Smooth - cytology; Muscle, Smooth - drug effects; Muscle, Smooth - metabolism; Original; Patch-Clamp Techniques; Pyloric Antrum - cytology; Pyloric Antrum - drug effects; Pyloric Antrum - metabolism; Rats; Rats, Sprague-Dawley; Ryanodine Receptor Calcium Release Channel - metabolism; Sarcoplasmic Reticulum - drug effects; Sarcoplasmic Reticulum - physiology
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1111/j.1469-7793.2000.00395.x

The intracellular calcium concentration ([Ca 2+ ] i ) was monitored in fura-2-loaded myocytes isolated from the rat gastric antrum and voltage clamped at −60 1r1rqmV1qusing the perforated patch clamp technique. The rate of quench of fura-2 fluorescence by Mn 2+ was used as a measure of capacitative Ca 2+ entry. Cyclopiazonic acid (5 μM) did not affect the holding current but produced a sustained elevation in steady-state [Ca 2+ ] i that was dependent on the presence of external calcium. Cyclopiazonic acid increased Mn 2+ influx with physiological external [Ca 2+ ], but not in Ca 2+ -free conditions. Cyclopiazonic acid increased the rate of [Ca 2+ ] i rise following a rapid switch from Ca 2+ -free to physiological [Ca 2+ ] solution. Sustained application of carbachol (10 μM) produced an elevation in steady-state [Ca 2+ ] i that was associated with an increased rate of Mn 2+ influx. Application of cyclopiazonic acid in the presence of carbachol further elevated steady-state [Ca 2+ ] i without changing Mn 2+ influx. Ryanodine (10 μM) elevated steady-state [Ca 2+ ] i either on its own or following a brief application of caffeine (10 m m ). Cyclopiazonic acid had no further effect when added to cells pre-treated with ryanodine. Neither caffeine nor ryanodine increased the rate of Mn 2+ influx. When brief applications of ionomycin (25 μ m ) in Ca 2+ -free solution were used to release stored Ca 2+ , ryanodine reduced the amplitude of the resulting [Ca 2+ ] i transients by approximately 30 %, indicating that intracellular stores were partially depleted. These findings suggest that continual uptake of Ca 2+ by the sarcoplasmic reticulum Ca 2+ -ATPase into a ryanodine-sensitive store limits the bulk cytoplasmic [Ca 2+ ] i under resting conditions. This pathway can be short circuited by 10 μ m ryanodine, presumably by opening Ca 2+ channels in the sarcoplasmic reticulum. Depletion of stores with cyclopiazonic acid or carbachol also activates capacitative Ca 2+ entry.