HYPERTONICITY, BUT NOT HYPOTHERMIA, ELICITS SUBSTANCE-P RELEASE FROM RAT C-FIBER NEURONS IN PRIMARY CULTURE

Isocapnic dry gas hyperventilation provokes hyperpnea-induced bronchoc onstriction in guinea pigs by releasing tachykinins from airway sensor y C-fiber neurons, It is unknown whether dry gas hyperpnea directly st imulates C-fibers to release tachykinins, or whether this physical sti mulus initiates a mediator cascade that indirectly stimulates C-fiber tachykinin release. We tested the hypotheses that mucosal hypothermia and/or hyperosmolarity-physical consequences of airway heat and water loss imposed by dry gas hyperpnea-can directly stimulate C-fiber tachy kinin release. Neurons isolated from neonatal rat dorsal root ganglia were maintained in primary culture for 1 wk, Cells were then exposed f or 30 min at 37 degrees C to graded concentrations of NaCl, mannitol, sucrose, or glycerol (0-600 mOsm) added to isotonic medium, or to isot onic medium at 25 degrees C without or with 462 mOsm mannitol added, F ractional release of substance P (SP) was calculated from supernatant and intracellular SP contents following exposure, Hyperosmolar solutio ns containing excess NaCl, mannitol, or sucrose all increased fraction al SP release equivalently, in an osmolarity-dependent fashion, In mar ked contrast, hypothermia had no effect on fractional SP release under isotonic or hypertonic conditions, Thus, hyperosmolarity, but not hyp othermia, can directly stimulate tachykinin release from cultured rat sensory C-fibers, The lack of effect of glycerol, a solute which quick ly crosses cell membranes, suggests that neuronal volume change repres ents the physical stimulus transduced by C-fibers during hyperosmolar exposure.