Embryonic Xenopus Culture Media (CM)

Components (mm)	Holtfreter's solution	Modified Barth's solution^a	Marc's modified Ringers^a	Normal amphibian medium^a	Steinberg's solution
NaCl	60.00^b	88.00	100.00	110.00	60.00^b
KCl	0.67	1.00	2.00	2.00	0.67
CaCl₂^c	0.90	0.41	2.00	—	—
Ca(NO₃)₂^c	—	0.33	—	1.00	0.34
MgCl₂^c	—	—	1.00	—	—
MgSO₄^c	—	0.82	—	1.00	0.83
EDTA	—	—	—	0.10	—
Sodium phosphate, pH 7.50	—	—	—	2.00	—
NaHCO₃	0.20^d	2.40	—	1.00	—
HEPES	4.60^d	10.00	5.00	—	10.00
pH	7.60	7.40	7.40	7.40	7.40
^aUse at half-strength (i.e., 0.5×) for culture media.
^bTo prevent animal caps from curling, increase the NaCl concentration from 60 mm to 90 mm. However, note that animal cap cells will differentiate into neural tissue autonomously when exposed to high NaCl concentrations.
^cOmit these components when preparing Ca²⁺/Mg²⁺-free culture media (CMFCM).
^dFor Holtfreter's Solution, use either NaHCO₃ or HEPES.
Sterilize the CM of choice by autoclaving for 20 min at 121°C. Add antibiotics such as kanamycin sulfate (0.1 g/L) to avoid bacterial contamination.