( ( ( ( ( ( Gating ( by ( internal ( Calcium ( Internal calcium ) ) ) ) ) ( ( ( is ( a ( second messenger ) ) ) ( -LRB- ( ( ( see ( ligand gating ) ) above ) -RRB- ) ) ) ( in ( many ( cell types ) ) ) ) ) , ) and ) ( thus ( ( channels ( gated ( by ( this ion ) ) ) ) ( can ( be ( ( characterized ( as ( ligand ( gated channels ) ) ) ) ( from ( the inside ) ) ) ) ) ) ) ) . )
(ROOT (S (S (S (VP (VBG Gating) (PP (IN by) (NP (JJ internal) (NNP Calcium) (NNP Internal) (NN calcium))))) (VP (VBZ is) (NP (DT a) (JJ second) (NN messenger)) (PRN (-LRB- -LRB-) (S (VP (VB see) (NP (JJ ligand) (NN gating)) (PP (IN above)))) (-RRB- -RRB-)) (PP (IN in) (NP (JJ many) (NN cell) (NNS types))))) (, ,) (CC and) (S (ADVP (RB thus)) (NP (NP (NNS channels)) (VP (VBN gated) (PP (IN by) (NP (DT this) (NN ion))))) (VP (MD can) (VP (VB be) (VP (VBN characterized) (PP (IN as) (NP (JJ ligand) (JJ gated) (NNS channels))) (PP (IN from) (NP (DT the) (NN inside))))))) (. .)))
Gating by internal Calcium Internal calcium is a second messenger (see ligand gating above) in many cell types, and thus channels gated by this ion can be characterized as ligand gated channels from the inside.
(ROOT (S (NP (NNP Calcium) (NNP ion)) (VP (VBZ is) (NP (NP (DT an) (NN example)) (PP (IN of) (NP (DT a) (JJ second) (NN messenger))))) (. .)))
Calcium ion is an example of a second messenger.