Professor Emeritus, Pacific Biosciences Research Center
Cellular mechanisms linking electrical and secretory activities of peptide-secretory cells, especially the role of calcium movements in control of secretion
In view of my impending retirement on July 31, 2010, my laboratory is not active and I am not accepting students except for directed reading. I am happy to advise on research questions regarding electrophysiological, cellular calcium measurement and immunofluorescence imaging techniques.
In recent work, currently being readied for publication, perforated patch-clamping techniques are used together with measurements of cell membrane capacitance, to characterize the ionic currents, particularly Ca2+, in relation to exocytotic secretion of prolactin from pituitary cells. The cells are dissociated from a species of fish having the capability of adapting to a wide range of salinities, the tilapia Oreochromis mossambicus. Prolactin functions in adaptation to hypoosmotic conditions and is released in direct response to reduction of medium osmolality. Further, in this species, the prolactin-secreting cells are segregated to a visually distinct lobe of the pituitary, facilitating their isolation. Imaged microfluorimetry with indicator vital dyes such as fura-2AM is being used to follow changes of cytoplasmic Ca2+ in these cells in response to hypoosmotic stimulation.
Earlier work exploited the large neurosecretory terminals of the crab X-organ - sinus gland to obtain the first intracellular recordings from secretory terminals; these revealed regenerative Ca2+-mediated impulses and spike broadening during repetitive activity. Patch-clamping of the crab secretory neurons in defined primary culture characterized voltage-gated Ca2+-channels of the somata and the terminals. The technique of isolating and recording from secretory terminals was later extended to mammalian neurohypophyseal terminals in other laboratories.
Still earlier work characterized the ionic currents giving rise to burst-forming potentials in lobster cardiac ganglion motorneurons. Intrinsic bursting is also a characteristic of many secretory cells. We found similar currents to those of the cardiac ganglion neurons responsible for bursting in crab secretory neurons and cultured rat vasopressin neurons.
Xu, S.-H., and I.M. Cooke (2007) Voltage-gated currents of tilapia prolactin cells. Gen. Comp. Endocrinol., 150: 219-232.
Bellinger, F.P., B.K. Fox, W.Y. Chan, L.K. Davis, M.A. Andres, T. Hirano, E.G. Grau, and I.M. Cooke (2006) Ionotropic glutamate receptor activation increases intracellular calcium in prolactin-releasing cells of the adenohypophysis. Am. J. Physiol. Endocrinol. Metab. 291: E1188-E1196.
Seale, A.P., J.C Fiess, T. Hirano, I.M. Cooke, and E.G. Grau (2006) Disparate release of prolactin and growth hormone from the tilapia pituitary in response to osmotic stimulation. Gen. Comp. Endocrinol., 145: 222-231.