Characterization of voltage-independent calcium channels in PC12 cells
Abstract
In eukaryotic cells, $\rm Ca\sp{2+}$ plays an important role in both electrical and biochemical signaling. Relatively small, transient increases of cytosolic $\rm Ca\sp{2+}$ can act to regulate many different cellular processes including neurotransmitter release, cellular growth, gene regulation and activation of $\rm Ca\sp{2+}$-dependent enzymes. Changes in cytosolic $\rm Ca\sp{2+}$ occurs via two pathways; release from intracellular stores and influx through $\rm Ca\sp{2+}$ channels. $\rm Ca\sp{2+}$ channels can be separated into two classes: voltage-dependent and voltage-independent. Compared with voltage activated channels, the voltage-independent channels are quite a recent discovery, and their biophysical properties, biochemical and physiological regulation, and physiological functions are poorly understood. PC12 cells, an adrenomedullary tumor cell line, provide an excellent system in which to study voltage-independent $\rm Ca\sp{2+}$-permeable channels (VICCs). In PC12 cells, VICCs were activated by patch excision, pertussis toxin, mastoparan, and nerve growth factor. Patch excision activates a small VICC with a slope conductance of 3 pS. The bacterial toxin, PTX and the wasp venom, mastoparan, alter the activity of GTP-binding proteins. Cell-attached patches from PC12 cells pretreated with PTX exhibited activity of two different inward $\rm Ca\sp{2+}$ channels: a small VICC, with properties that were similar to the excision-activated channel (3 pS), and a second, larger VICC (17 pS). Two channels with similar properties could also be observed with mastoparan (10 uM) in the recording pipette. These results suggest that two VICCs can be activated by several different pharmacological agents that affect G-proteins. Interestingly, two VICCs with very similar properties can also be activated by including NGF (2 nM) in the recording pipette. Thus the data suggest that several pathways may be converging on and activating the same set of VICCs (3 pS and 17 pS). In PC12 cells, these channels are activated by patch excision, PTX, mastoparan and NGF. These channels may actually be activated by intracellular or extra-cellular ligands, assuming that the ligand acts in an indirect manner by removing effects of the cytoplasmic inhibitor.
Degree
Ph.D.
Advisors
Strong, Purdue University.
Subject Area
Neurology|Cellular biology|Molecular biology
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