Calcium ions serve as intracellular messengers for a wide range of cellular functions, spanning time scales ranging from milliseconds to hours, days or even weeks. We are studying the cellular and molecular mechanisms underlying the generation and transduction of several responses mediated by intracellular Ca²⁺ in skeletal muscle fibers, sympathetic ganglion neurons and in cell culture systems.

Generation of the Ca²⁺ transient in skeletal muscle:
Skeletal muscle is activated within a few ms after membrane depolarization by a massive release of Ca²⁺ ions from the intracellular storage location, the sarcoplasmic reticulum. We are studying three steps in the activation mechanism for Ca²⁺ release in isolated single functioning skeletal muscle fibers: (1) Activation of membrane voltage sensor molecules, studied electrophysiologically by the resulting "gating current" ; (2) Opening patterns of individual Ca²⁺ release channels or of a group of a few functionally linked release channels in response to depolarization or ligand activation, detected by laser scanning confocal microscopy as highly localized calcium "sparks"; (3) the mechanism coupling the voltage sensors to the release channels, studied by pharmacological and biochemical manipulation in functioning fibers. (supported by NIH/NINDS grant "Excitation-contraction coupling in cut muscle fibers")

Molecular basis of skeletal muscle fiber types:
In another project we are studying the molecular mechanisms underlying functional differences in mammalian fast-twitch and slow-twitch skeletal muscle fibers, which differ in the speed of contraction and relaxation and which express different isoforms of most muscle-specific proteins. The qualitative and quantitative differences in protein expression and how such differences underlie the differences in the generation and transduction of the [Ca²⁺] transients in the two fiber types is being investigated in muscle fibers acutely isolated from adult muscle and in isolated fast- and slow-twitch fibers maintained in cell culture. (supported by NIH/NINDS grant "Calcium removal and regulation of muscle function")

Calcium signalling in neurons:
Mechanisms of Ca²⁺ signalling in neurons are being investigated in neurons isolated from sympathetic ganglia and maintained in culture. Topics currently under examination in our lab include mechanisms for terminating the cytosolic [Ca²⁺] signal and the spatial location of the intracellular store from which Ca²⁺ ions are released. (supported by NIH/NINDS grant "Calcium removal and regulation of muscle function").

Calcium homeostasis in dystrophic muscle fibers:
The fiber isolation and culture methods developed in our lab (above) are also being used to investigate the basis of differences in calcium homeostasis in muscle fibers isolated from normal and dystrophic mice. Dystrophic mice lack the muscle cytoskeletal protein dystrophin, which is also absent in human Duchenne muscular dystrophy and may provide mechanical support for the muscle fiber membrane. (supported by the Muscular Dystrophy Association).