Ca2+ influx activated by low pH in Chlamydomonas

Area of Science:

• Cell Biology
• Biophysics
• Physiology

Background:

• Cytosolic acidification in Chlamydynamics induces calcium (Ca2+) influx, leading to flagellar shedding.
• The precise Ca2+ influx pathways mediating different cellular responses, including deflagellation and photoresponses, remain unclear.

Purpose of the Study:

• To investigate the specific Ca2+ influx pathway responsible for deflagellation induced by cytosolic acidification.
• To differentiate this pathway from Ca2+ influxes involved in phototaxis and photophobic responses.

Main Methods:

• Utilized Chlamydynamics mutants (bald-2, fa-1) and isolated flagella to determine pathway localization.
• Assessed Ca2+ influx using pharmacological blockers (Cd3+, Cd2+, SKF-96365, flufenamic acid) and colchicine to inhibit flagellar assembly.
• Monitored the transient inactivation and recovery of the Ca2+ influx pathway after acid exposure and deflagellation.

Main Results:

• The acidification-stimulated Ca2+ influx pathway is not located on the flagellar membrane.
• This pathway is potently blocked by Cd3+ but insensitive to Cd2+ and organic Ca2+ channel blockers.
• Acidification-stimulated Ca2+ influx is transiently inactivated following flagellar shedding in wild-type cells, an effect not seen in the fa-1 mutant.
• Pathway recovery occurs within 30 minutes and does not require flagellar reassembly.

Conclusions:

• The deflagellation-inducing Ca2+ influx pathway is a distinct Ca2+ entry mechanism, separate from known Ca2+ channels.
• Pathway regulation, drug sensitivity, and localization differentiate it from Ca2+ influxes in other Chlamydynamics photoresponses.
• Deflagellation itself, rather than acidification or Ca2+ influx, appears to trigger the transient inactivation of this pathway.