Hemispheric asymmetry of rapid chloride responses to inositol trisphosphate and calcium in Xenopus oocytes

Abstract

Shallow injection of inositol 1,4,%trisphosphate (IP,) near the animal pole of the Xenopus oocyte resulted in a large depolarizing current that decayed rapidly. A similar injection near the vegetal pole produced a much smaller response characterized by a significantly slower rate of decay. Injection of CaCI, near the animal pole of the oocyte resulted in a large depolarizing current characterized by rapid rise and decay times. Injection near the vegetal pole of the cell produced responses that exhibited similar amplitudes but much longer rise and decay times. The protein kinase C (PK-C) activator, &phorbol 1Zmyristate 13-acetate (PMA), significantly enhanced the rapid responses to IP, injections at either hemisphere but did not affect the amplitudes of the responses to CaCb. The PK-C inhibitor I-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7) had no effect on the responses to CaClr. These results imply an asymmetric distribution of calcium stores and chloride channels between the two hemispheres of the oocyte.

Calcium wave evoked by activation of endogenous or exogenously expressed receptors in Xenopus oocytes.

“…In parallel with the Ca2+ imaging, we voltage-clamped the oocytes; the results obtained were consistent with the imaging data in that all the above agonists evoked responses that are believed to depend on inositol trisphosphate-mediated release of intracellular Ca2 , which in turn activates chloride channels (2,(4)(5)(6). The number of agonist-responsive oocytes detected electrophysiologically was similar to that found by imaging.…”

“…When the translated mRNA produces a receptor or ion channel, it is usually biochemically functional, exhibiting the appropriate pharmacological and electrophysiological properties. A number of recent studies have dealt with de novo expression of neurotransmitter receptors, as detected by electrophysiological and biochemical methods (2)(3)(4)(5), making the oocyte an excellent system to detect newly expressed ion channels or ion channel-linked receptors in cloning strategies.…”

Interaction between capacitative Ca2+ influx and Ca2+-dependent Cl− currents inXenopus oocytes

“…Ca 2+ -activated C1-channels are also thought to be clustered into the animal pole [26] and perhaps even clustered in regions of different densities within this pole [27]. Several findings support the idea that C1-channels are clustered.…”

Use ofXenopus oocytes for the functional expression of plasma membrane proteins

“…Nonrandom distribution of any of the components involved in signal transmission, distal to the receptor, would conceivably result in a locally different response upon application of agonist. It has indeed been shown that injection of IP3 at the animal pole elicits much larger currents than at the vegetal pole [19,135], whereas conflicting reports have been published on an asymmetry of the response to injection of calcium [135,150]. Dreyfus et al [44] studied the distribution of a membrane-associated butyrylcholinesterase after injection with cDNA-derived mRNA.…”