Certain calcium channel inhibitors exhibit a number of secondary effects on the physiological properties in Nitellopsis obtusa: a voltage clamp approach.

An unsolved problem of contemporary plant electrophysiology is the identity of Ca2+ channels responsible for the initiation of the action potential. We took a pharmacological approach and applied several Ca2+ channel blockers (verapamil, tetrandrine, and NED-19) on a Characean (Nitellopsis obtusa) algae model system. The impact of the selected pharmaceuticals on the parameters of excitation transients of a single cell was analysed employing the two-electrode voltage clamp technique. It was revealed that tetrandrine exerted no effect, while both verapamil and NED-19 prolonged activation and inactivation durations of the excitatory Cl− current. NED-19 also significantly depolarised the excitation threshold membrane potential and shifted Ca2+ current reversal potential. Thus, NED-19 most specifically targeted Ca2+ channels. A viability assay paired with observations of cytoplasmic streaming revealed that verapamil affected not only Ca2+ channels but also exhibited non-specific effects, which eventually lead to cell death. Since many potential Ca2+ channel blockers exert additional undesirable non-specific effects, our study underlines the necessity to search for new more specific modulators of plant Ca2+ transport systems. It is challenging to isolate transmembrane Ca2+ currents that are activated during the generation of action potentials in plants. We applied several different Ca2+ channel blockers (verapamil, tetrandrine, and NED-19). It was found that, while verapamil and NED-19 did affect Ca2+ currents, non-specific effects were also observed, compromising the usage of these blockers as selective means of distinguishing Ca2+ currents in plants. [ABSTRACT FROM AUTHOR]