Ian M. Cooke

PhD Harvard (Biology), 1962

Professor, Department of Zoology
Researcher, Békésy Laboratory of Neurobiology (PBRC)

ian@pbrc.hawaii.edu
www.pbrc.hawaii.edu/ian

Cellular control of secretion from neurons and endocrine cells

Early studies of secretion and synaptic transmission showed an essential role of calcium ions (Ca2+) in stimulus-secretion coupling. We are studying, at the level of single cells, how electrical responses lead to entry of Ca2+ and other ions, how the Ca2+ is disposed of and how Ca2+ and other ions regulate the cellular machinery of secretion and its related processes.
We are using recently developed techniques that permit controlling membrane voltage and measuring ionic currents (patch clamping) and microscopy with fluorescent dyes, such as fura-2, which indicate intracellular Ca2+ concentration. Secretion from single cells under patch clamp is monitored by changes in their electrical capacitance: an increase occurs when storage granules fuse and open (exocytosis), thereby increasing the surface area. Amperometry, in which a polarized carbon fiber electrode produces a current when secreted substances, such as serotonin, are oxidized, can detect secretion from single cells.

Our laboratory has been working for many years with the neurosecretory system of the crab eyestalk. This preparation offers a purely peptide-secretory system that is easily isolated and has large neurons and large secretory terminals; the neurons are amenable to dissociation and culturing; and the cultured neurons are identifiable as to the hormone they produce by their outgrowth morphology. Our recent work on the voltage-operated Ca2+ channels of such neurons and their terminals revealed a single type of Ca2+ channel (where most neurons have several) which, because it is resistant to certain drugs and toxins, is representative of an important, but poorly characterized, type of vertebrate brain Ca2+ channel. In collaboration with a molecular biologist, we have begun work to clone and sequence the crab Ca2+ channel.

A new line of investigation is the electrical and Ca2+ -signalling associated with secretion of prolactin from endocrine cells of the fish adenohypophysis. Building on observations from Dr. Grau' s laboratory showing direct, sensitive regulation of secretion by osmolarity, we wish to characterize this most direct of secretory reflexes. We anticipate that this will involve stretch-activated ion channels.

Representative publications:

Duan S, Cooke IM. 1999. Glutamate and GABA activate different receptors and Cl- conductances in crab peptide-secretroy neurons. J Neurophysiol. in press.

Meyers DER, Cooke IM. 1997. Comparison of Ca2+ currents of peptidergic neurons developing differing morphology with time in culture. J Exp Biol 200:723-733.

Richmond JE, Codignola A, Cooke IM, Sher E. 1996. Calcium- and barium-dependent secretion from the rat insulinoma cell line RINm5F: evidence from capacitance tracking and serotonin release. Pflügers' Arch 432:258-269.

Richmond JE, Penner R, Keller R, Cooke IM. 1996. Characterization of the calcium current in isolated terminals of crustacean peptidergic neurons. J Exp Biol 199:2053-2059.

Keller R, Grau S, Cooke IM. 1995. Quantitation of peptide hormone in single cultured secretory neurons of the crab, Cardisoma carnifex. Cell Tissue Res 281:525-532.

Richmond JE, Sher E, Cooke, IM. 1995. Characterization of the Ca2+ current in freshly dissociated crustacean peptidergic neuronal somata. J Neurophysiol 73:2357-2368.

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