Effects of different ionic environments on the mechano-sensitivity of lateral line organs in the mudpuppy

Abstract

1. The lateral line organ ofNecturus maculosus was stimulated with water vibrations, and the degree of synchronization between stimulus and afferent activity was related to the ionic composition of the external solution. 2. The mechano-sensitivity was a function of the Ca++ concentration of the external medium (Fig. 2). The organs were insensitive to vibrations in Ca++ free solution (containing Ca-chelating agents) (Fig. 5), whereas the sensitivity leveled off at a maximum value for concentrations above about 1 mM Ca++. The effect of Sr++ was similar to Ca++ (Fig. 4). K+ and Na+ also enhanced the mechano-sensitivity, but the effect of these ions was much less than for Ca++ (Fig. 3). 3. The mechano-sensitivity was suppressed by Mg++, Co++ and La+++ (Figs. 7, 8), the order of effectiveness being La+++≫ Co++> Mg++. The suppression decreased with increasing Ca++ concentration, suggesting that the effect of Ca++ is competitively blocked by these ions. The mechano-sensitivity was also suppressed by low pH (Fig. 9). 4. The different ions tested in the present study affected the generation of hair cell receptor potentials, and it is suggested that the inward depolarizing receptor current of hair cells in mudpuppy lateral line organs is mainly carried by Ca++.