K+ and Ca++ in the receptor lymph of arthropod cuticular mechanoreceptors.

Two types of cuticular strain detectors, the campaniform sensilla on the haltere of the blowfly, Calliphora vicina, and the slit sensilla on the tibia of the spider, Cupiennius salei, were investigated. In campaniform sensilla a transepithelial voltage (43.6 +/- 10.7 mV), which depends on an intact metabolism, occurs. In spider slit sensilla no transepithelial voltage exists. The occurrence and the lack of a transepithelial voltage is paralleled with differences in the ionic composition of the receptor lymph in the two arthropod sensilla. We used double-barrelled ion-selective microelectrodes to measure potassium and calcium content in the receptor lymph with respect to the hemolymph. The potassium concentration in campaniform sensilla (121 +/- 15 mM) is five times larger than that of the wing hemolymph (25 +/- 7 mM) and nine times larger than that of the haltere hemolymph (13 +/- 3 mM). These differences are statistically significant. The calcium concentration in campaniform sensilla (0.8 +/- 0.5 mM) does not differ significantly from that of the hemolymph (1.2 +/- 0.7 mM). In spider slit sensilla no significant difference occurs between the potassium concentration of the receptor lymph (9.5 mM +/- 5.5 mM) and that of the hemolymph (8 +/- 3 mM). The calcium concentration of the hemolymph (1.6 +/- 0.9 mM) is 3 times higher than that of the receptor lymph (0.6 +/- 0.3 mM). This difference is significant.