| Research Abstract |
To elucidate the role and the regulatory mechanism of cytosolic Ca^<2+> concentrations ([Ca^<2+>]_i), we have measured [Ca^<2+>]_i and the membrane currents or membrane potentials in hypothalamic supraoptic nucleus (SON) neurons, adrenal chromaffin cells, and melanotrophs of the pituitary pars intermedia.
The results of the study are following :
1. The peptide PACAP increased [Ca^<2+>]_i in rat SON neurons by increasing Ca^<2+> entry. 2. In bovine adrenal chromaffin cells, PACAP induced both Ca^<2+> entry and Ca^<2+> release. 3. In rat melanotrophs, PACAP induced Ca^<2+> entry. 4. In bovine adrenal chromaffin cells, the peptide PAMP inhibited nicotinic currents and [Ca^<2+>]_i rises induced by nicotine. 5. GABA_B receptors were present in the presynaptic sites of the SON and inhibited both GABA and glutamate release. 6. Angiotensinll inhibited outwardly rectifying K^+ currents in SON neurons. 7. The AT1 antagonist losartan partially blocked electrically evoked synaptic currents in SON sl
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ices. 8. peptide adrenomedullin increased [Ca^<2+>]_i and modulated the firing of SON neurons. 9. GABA_B receptors were also present in the postsynaptic sites of the SON and inhibited voltage-gated Ca^<2+> currents. 10. Glutamate and its analogues increased [Ca^<2+>]_i and quisqualate and trans ACPD,agonists for metabotropic glutamate receptors, stimulated Ca^<2+> release in SON neurons. 11. Prostaglandin E_2 (PEGE_2) directly acted on SON neurons to induce [Ca^<2+>]_i rises and membrane depolarization, whereas interleukin 1beta did not have direct effect. 12. PGE_2 inhibited Ca^<2+> currents in rat melanotrophs through EP1, EP3, pertussis toxin sensitive G-proteins. 13. PACAP induced Ca^<2+> release from rynanodine-sensitive Ca^<2+> stores of bovine adrenal chromaffin cells. 14. There was a good correlation between spontaneous Ca^<2+> oscillations and phasic bursting in SON neurons. 15. Angiotensinll increased [Ca^<2+>]_i through losartan-sensitive AT1 receptors in rat subfornical organ neurons. Less
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