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Effects of cyclic nucleotides and calcium on transduction and encoding processes in frog muscle spindle
M Sokabe1, N Fujitsuka, A A Kori
1Department of Physiology, Nagoya University School of Medicine, Japan.
Abstract:
In decapsulated muscle spindles, application of dibutyryl cyclic AMP (d-cAMP, 0.1-10 mM) and forskolin (10-100 microM) increased the rate of spontaneous discharges and decreased the responsiveness to stretch. Addition of 2-5 mM CaCl2 or 0.5-2 mM BaCl2 to the above drugs prevented the deterioration of the responsiveness to stretch and the increase in the rate of spontaneous discharges. Similar changes in the afferent discharges were observed with application of isobutylmethyl-xanthine (IBMX, 0.5-2 mM) or carbonyl cyanide chlorophenylhydrazone (CCCP, 1-10 microM). Application of 0.1-1 mM quercetin resulted in a prolonged increase in the discharge rate, lasting 15-20 s after the release of stretch. These results suggest that cAMP is involved in the regulation of the sensory processes through a modification of intracellular calcium activity.
Insights
Cyclic AMP (cAMP) influences muscle spindle sensory function by altering intracellular calcium. This research reveals how cAMP-modulating drugs affect muscle afferent discharges and stretch responses.
Area of Science:
- Neuroscience
- Muscle Physiology
- Cellular Signaling
Background:
- Muscle spindles are sensory receptors crucial for proprioception and motor control.
- The role of intracellular signaling pathways, such as cyclic AMP (cAMP), in regulating sensory receptor function is not fully understood.
Purpose of the Study:
- To investigate the involvement of cAMP in the regulation of muscle spindle afferent discharges.
- To explore the interaction between cAMP and intracellular calcium activity in sensory processes.
Main Methods:
- Experiments were conducted on decapsulated muscle spindles.
- Application of dibutyryl cyclic AMP (d-cAMP), forskolin, isobutylmethyl-xanthine (IBMX), carbonyl cyanide chlorophenylhydrazone (CCCP), and quercetin were used to modulate cAMP levels and cellular activity.
- Changes in spontaneous discharge rates and responsiveness to stretch were recorded.
Main Results:
- Dibutyryl cyclic AMP (d-cAMP) and forskolin increased spontaneous discharges and reduced stretch responsiveness.
- Calcium chloride (CaCl2) and barium chloride (BaCl2) mitigated these effects, suggesting a role for calcium.
- IBMX, CCCP, and quercetin also induced changes in afferent discharges, further implicating intracellular signaling pathways.
Conclusions:
- Cyclic AMP (cAMP) plays a significant role in regulating muscle spindle sensory processes.
- The effects of cAMP appear to be mediated through modulation of intracellular calcium activity.
- These findings provide insights into the molecular mechanisms underlying sensory transduction in muscle spindles.