ABSTRACT
Physiological Conditions .................................................................. 137 6.4 Recording of Voltage-Gated Ca2þ Current ................................................. 137 6.5 Perforated Patch Recordings........................................................................ 139 6.6 Estimate of Single Ca2þ Channel Conductance.......................................... 140
6.6.1 Single-Channel Recording ................................................................ 140 6.6.1.1 Voltage-Gated Ca2þ Channels ........................................... 141 6.6.1.2 Store-Operated Ca2þ Channels .......................................... 141
6.6.2 Fluctuation Analysis ......................................................................... 142
6.7 Total Internal Reflection Fluorescence Microscopy: A New
Tool for Studying Ca2þ Channels ............................................................... 143 Acknowledgments ................................................................................................ 144
References............................................................................................................. 144
The opening of plasmalemmal Ca2þ channels has profound effects on cell function. First and most importantly, an increase in cytoplasmic Ca2þ concentration is used as a key signaling messenger in virtually every cell through the phylogenetic tree,
where it regulates a diverse array of fundamental physiological processes such as
neurotransmitter release, muscle contraction, gene transcription, and cell growth
and proliferation [1]. Second, when a Ca2þ channel opens, the inward flux of Ca2þ
often depolarizes the membrane potential thereby affecting membrane excitability
[2]. Finally, Ca2þ channels have fundamental roles in cell signaling that do not require ion permeation. In the T-tubules of skeletal muscle, the intracellular domain
between loops II and III of the L-type calcium channel (Cav 1.1) can physically
interact, ostensibly via the intermediary protein triadin, with ryanodine type I
receptors in the sarcoplasmic reticulum. Depolarization of the T-tubules results in
a conformational change in the L-type, that is, channel propagated rapidly to the
ryanodine receptor, resulting in Ca2þ release [3]. Two major classes of Ca2þ-selective channel are known to exist. Voltage-gated
Ca2þ channels are found in excitable cells like nerve and muscle, but are largely excluded from nonexcitable cells. Voltage-gated Ca2þ channels regulate synaptic transmission, muscle contraction and gene transcription [2]. Store-operated Ca2þpermeable channels are a major source of Ca2þ in nonexcitable cells, where they control a diverse range of functions including secretion, enzyme activity, and cell
growth and proliferation [4]. Store-operated Ca2þ channels are unique among known plasmalemmal ion channels in that they are specifically activated by the
process of emptying the intracellular Ca2þ stores [4]. How this is accomplished remains contentious.
