Biomedical subjects

G Matthews

Publications and source records attributed to G Matthews.

147 records · Page 9Linked to original sources

PubMedDate not supplied

Identification of sodium channel subtypes induced in cultured retinal pigment epithelium cells.

Recent electrophysiological experiments have shown that retinal pigment epithelium (RPE) cells begin to produce neuronal-type voltage-dependent sodium currents when placed in dissociated cell culture. In this study, the sodium channel types induced in cultured rat RPE cells were identified. Sodium channel mRNAs encoding two distinct alpha subunits were detected in the cultured RPE cells, brain type II/IIA, and a novel rat mRNA which we have termed RET1. These two sodium channel types may correspond to the TTX-sensitive and TTX-insensitive components of sodium current reported previously in cultured rat RPE cells.

Amino Acid Sequence↗

PubMedDate not supplied

Calcium action potentials in retinal bipolar neurons.

Patch-clamp and calcium-indicator measurements were used to examine the electrical excitability of large-terminal bipolar neurons from goldfish retina. Large, transient increases in intracellular calcium occurred spontaneously in the synaptic terminal but not in the soma of bipolar neurons. Calcium transients were blocked by hyperpolarization, by external application of calcium-channel blockers, and by the neurotransmitters GABA and glutamate. These observations suggest that calcium action potentials are responsible for the spontaneous increases in intraterminal calcium, which was directly confirmed by electrical recordings of calcium-dependent action potentials in both whole-cell and perforated-patch recordings. We suggest that regenerative depolarization produced by the opening of calcium channels in the synaptic terminal of on-type bipolar neurons represents an amplification mechanism in the high-sensitivity ON pathway in the dark-adapted fish retina.

Action Potentials↗

PubMedDate not supplied

Rapid calcium-current kinetics in synaptic terminals of goldfish retinal bipolar neurons.

Onset and offset of calcium current in response to short, depolarizing voltage pulses were studied in giant synaptic terminals of goldfish bipolar neurons. Tail-current decays were extremely rapid (80 micros at -70 mV), and exponentially slowed at more positive repolarization potentials. The amplitude of tail current following voltage pulses varied with the pulse amplitude, according to a Bolzmann distribution with a V1/2 of -27.6 mV and a slope factor of 13.8 mV. When interpreted with a Hodgkin-Huxley model, calcium-current onset was best described by m2 kinetics and a time constant (tau(m)) of 0.62 ms at -10 mV. The kinetics of calcium-current onset and offset are at least two- to threefold faster than those described in other native cells. Combined with other recent data, the results suggest that the rapid kinetics may participate in a fast signaling mode in the goldfish ON-center pathway.

Animals↗