Distribution of calcium in the suctorian Discophrya collini: an x-ray microanalytical study

Intracellular calcium transients in suctorian protozoa (Trichophrya spp.): correlation with spontaneous tentacle contractions

The luminescent photoprotein aequorin was used to measure intracellular free Ca2+ in three species of suctorian protozoon, Trichophrya riederi, Trichophrya collini and Trichophrya rotunda. Resting [Ca2+]i ranged from about 75-110 nM, and was unaffected by a change in temperature of the perfusate. Spontaneous Ca2+ transients were observed in all three species, with peak amplitudes ranging from 100-600 nM. In T. riederi and T. rotunda, three categories of transient (small, intermediate, large) were recorded; T. collini displayed only small transients. In both T. riederi and T. collini, raising the temperature from 5 degrees to 26 degrees C led to an increase in the frequency of transients. Furthermore, in T. riederi, large transients occurred only at the higher temperature. The frequency of spontaneous contractions of the tentacles of T. riederi was also temperature-dependent. Increasing the temperature over the range 5-26 degrees C led to a concomitant increase in contraction frequency and a decrease in mean tentacle length. The possible mechanisms of spontaneous Ca2+ transient generation and their role in the control of contraction are discussed.

Tentacle contraction in Heliophrya erhardi (Suctoria): the role of inositol phospholipid metabolites and cyclic nucleotides in stimulus-response coupling

Extracellular stimulation of Heliophrya erhardi with 15 V, 100 ms induces tentacle contraction. The effects of a number of pharmacological agents on response latency (time from stimulus to start of contraction) and contraction time (time for tentacles to reach 20% of their original length) were recorded. Contraction was enhanced in the presence of phorbol ester TPA and R59022, both of which increase activation of diacylglycerol-dependent protein kinase C. Lithium ions, which are known to inhibit dephosphorylation of inositol 1-phosphate, also affected the response, causing a decrease in latency and increase in contraction time. These results strongly implicate products of inositol phospholipid metabolism in stimulus-contraction coupling. The latency of contraction was reduced in the presence of IBMX, a nonspecific inhibitor of cyclic nucleotide phosphodiesterases. Application of membrane-permeable cyclic nucleotide analogs led to an increase in latency and contraction time for cAMP analog, but a decrease in both parameters for cGMP. This suggests that the two cyclic nucleotides have opposing roles in modulating the response. The possible roles and interactions of membrane phospholipid metabolites and cyclic nucleotides in the control of tentacle contraction of H. erhardi are discussed.