Activation of 5-HT3 receptors expressed in Xenopus oocytes does not increase cytoplasmic Ca2+ levels.
The wildtype 5-HT3 receptor was expressed in Xenopus oocytes from a cloned cDNA. Two-electrode voltage-clamp and fura-2 techniques were used simultaneously to monitor the current induced by the activation of the 5-HT3 receptor and the cytoplasmic Ca2+ concentration ([Ca2+]i). The application of serotonin (5-HT; 50 microM) in a physiological bathing solution containing Ca2+ (1.8 mM) elicited inward currents of up to approximately 1.3 microA at a potential of -90 mV. There was little or no detectable change in [Ca2+]i. In experiments on oocytes bathing in a nominally Ca(2+)-free medium, the injection of (2,4,5)IP3, an analog of inositol 1,4,5-trisphosphate ((1,4,5)IP3), produced a large increase in [Ca2+]i levels due to the liberation of Ca2+ from intracellular stores. This response was followed by a sustained elevation of [Ca2+]i upon restoring extracellular Ca2+ (i.e. capacitative Ca2+ entry). Furthermore, when calcium-permeable heteromeric (NR1/NR2A) N-methyl-D-aspartate (NMDA) receptors were expressed in oocytes, the activation of these receptors led to a large increase in [Ca2+]i in a Ca(2+)-containing external medium. It is concluded that wildtype 5-HT3 receptors expressed in Xenopus oocytes and studied under conditions used here show little or no permeability for Ca2+.
Gilon
P
P
Laboratory of Cellular and Molecular Pharmacology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, N.C. 27709, USA.
Yakel
J L
JL
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism*; D008564:Membrane Potentials; D009865:Oocytes / Q000378:metabolism* / Q000502:physiology; D011985:Receptors, Serotonin / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D044406:Receptors, Serotonin, 5-HT3; D012701:Serotonin / Q000494:pharmacology; D014982:Xenopus laevis
D011985:Receptors, Serotonin; D044406:Receptors, Serotonin, 5-HT3; D012701:Serotonin; D002118:Calcium