Different pathways by which extracellular Ca2+ promotes calcitonin gene-related peptide release from central terminals of capsaicin-sensitive afferents of guinea pigs: effect of capsaicin, high K+ and low pH media.
Different modes by which Ca2+, entering the nerve terminal, promotes transmitter secretion as well as the ability of protons to release neuropeptides, have been shown in peripheral endings of capsaicin-sensitive afferents. We have studied these two aspects in the central endings of these neurons by measuring the release of calcitonin-gene related peptide-like immunoreactivity (CGRP-LI) from slices of the dorsal half of the guinea pig spinal cord. Although capsaicin (1 microM) released both CGRP-LI and substance P-like immunoreactivity (SP-LI), CGRP-LI was chosen as the sole suitable marker of peptides released from central terminals of capsaicin-sensitive afferents, since after in vitro desensitization to capsaicin (1 microM capsaicin for 20 min), high K+ (80 mM) failed to evoke CGRP-LI release, whereas SP-LI release was still observed. The capsaicin (1 microM)-evoked CGRP-LI release was entirely dependent on extracellular Ca2+. It was unaffected by 0.3 microM tetrodotoxin (TTX), slightly reduced by 0.1 microM omega-conotoxin (CTX) and blocked by 10 microM Ruthenium red (RR). The Ca(2+)-dependent K+ (80 mM)-evoked CGRP-LI release was unaffected by TTX, markedly reduced by CTX and only moderately inhibited by RR. Low pH (pH 5) produced a remarkable increase in CGRP-LI outflow that was abolished after exposure to capsaicin, reduced by about 50% in Ca(2+)-free medium and unaffected by TTX (0.3 microM). The Ca(2+)-dependent component of the proton-evoked CGRP-LI release was abolished in the presence of RR (10 microM) and slightly inhibited by CTX (0.1 microM).(ABSTRACT TRUNCATED AT 250 WORDS)
Del Bianco
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E
Institute of Internal Medicine IV, University of Florence, Italy.
Santicioli
P
P
Tramontana
M
M
Maggi
C A
CA
Cecconi
R
R
Geppetti
P
P
D000344:Afferent Pathways / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002211:Capsaicin / Q000494:pharmacology*; D004357:Drug Synergism; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008297:Male; D009411:Nerve Endings / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D010456:Peptides, Cyclic / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D012430:Ruthenium Red / Q000494:pharmacology; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D020960:omega-Conotoxins
D002121:Calcium Channel Blockers; D010456:Peptides, Cyclic; D020960:omega-Conotoxins; C053423:Conus magus toxin; D012430:Ruthenium Red; D013779:Tetrodotoxin; D015740:Calcitonin Gene-Related Peptide; D011188:Potassium; D002211:Capsaicin; D002118:Calcium