Ciliary and flagellar activity control in eukaryotic cells by second messengers: Calcium ions and cyclic nucleotides

Extracellular stimuli are converted in eukaryotic cells through signal tran sduction mechanisms to generate intracellular second messengers such as cyc lic nucleotides and Ca2+. These molecular signals, amongst other, may contr ol the ciliary and flagellar locomotor systems by modulating the activity o f axonemes, changing the direction and frequency of effective ciliary beati ng or changing the pattern of flagellar motion. The primary role in regulat ing the mechanisms of axonemal motility by second messengers is played by p rocesses of phosphorylation and dephosphorylation of axoneme proteins. Ca2 may also regulate the levels of cAMP and cGMP by controlling the activity of cAMP and cGMP cyclases. In addition, Ca2+ and cyclic nucleotides may reg ulate ion channel conductance, thus affecting the cell membrane potential i n these cells.